1. Field of the Invention
The invention generally relates to a digital audio or video player or recorder and, more specifically, to a method of and a system for protecting the copyright of a program recorded on a storage medium such as a video tape, an optical disc, semiconductor memory, etc. in such a player or a recorder.
2. Description of the Prior Art
A variety of copy protecting schemes for various recording media have been proposed so far. In Digital Audio Tape (DAT) recorders for-example, the Serial Copy Management System is used in which copy operation is controlled such that an-original DAT tape is permitted to be copied only once.
As one of such copy protecting schemes, there is also known the Copy Generation Management System (CGMS) that uses two-bit copy generation management signals or flags. In this system, if the value of the two-bit signals recorded on a recording medium is “00”, then the copying of the recording medium is permitted unlimitedly; if “10”, then the copying is permitted only once; and if “11”, then the copying is prohibited. In the above-mentioned case of “10” in the two-bit signals, the copying involves a change of the value of the two-bit signals from “10” to “11”.
In one copy protection scheme used in video recorders that stores, on a recording medium, a transport stream (TS) based on the MPEG-2 (Moving Picture Experts Group phase 2) standard, a digital water mark is embedded in the transport stream in recording operation. The water mark is detected in playing operation to determine whether the recording medium should be played.
However, if a recorded recording medium is copied by using a player and a recorder, then any of the above mentioned authentication signals, i.e., the Serial Copy Management signal, the two-bit copy generation management signals and the digital water mark will be transferred from the player to the recorder. This gives an attacker a chance to counterfeit such the transferred authentication signal(s) such that the counterfeited authentication signal(s) has a value indicative of permission to copy the recording medium, permitting the attacker to make copies of the recording medium.
One solution to this problem was given by U.S. Pat. No. 5,659,613, which discloses “Method and apparatus for copy protection for various recording media using a video finger print”. The method and apparatus use a combination of a Video Finger Print Signal and an Authenticating Signature to permit the player to handle either copy-protected or non-copy-protected media, in a manner that is difficult to compromise. The patent is hereby incorporated by reference.
However, it is preferable for the recording media player and/or recorder to have a higher copy protection capability. Though the higher the better, if the system becomes the more complicated, it won't be desirable. It is also preferable for the recording media player and/or recorder to have a high degree of flexibility in dealing with recording media of various copy conditions such as a freely copy-able type, a one-generation copyable type (or a type having a one-time copy permission and having not been copied), a play-only type, and a pirated and even-play-prohibited type.
It is therefore an object of the invention to provide a recording media player and a recording media recorder provided with a high-security copy protection system of less complexity.
It is another object of the invention to provide a recording media player and a recording media recorder provided with a copy protection system stubborn to attacks and highly flexible in dealing with recording media of various copy conditions.